This free program was originally created by FullScreensavers. This free PC program was developed to work on Windows XP, Windows Vista, Windows 7, Windows 8 or Windows 10 and is compatible with 32-bit systems. The following versions: 2.1 and 1.0 are the most frequently downloaded ones by the program users.

From the developer:

FullScreensavers is pleased to present new colorful screensaver of the underwater world.

You may want to check out more software, such as Aqua Castles, 3D Haunted Castle ScreenSaver or Dolphin Aqua Life Screensaver, which might be similar to Aqua Castles Screensaver.